EXTERNAL ANATOMY 25 



The hypodermis is a single layer of pavement epithelium or 

 cuboidal cells. It is the living part of the body-wall and excretes 

 the cuticle and the wax in which the body is imbedded or by which 

 it is covered. The wax varies in form according to its method of 

 excretion. In such genera as Ceroplastes and Tachardia, where 

 the wax is a homogenous mass, it is considered as excreted by all 

 of the hypodermal cells and as poured out through the cuticle. 

 In most coccids the wax is excreted by special cells of the hypo- 

 dermis which have been greatly modified and enlarged. Careful 

 detailed studies of the form of the wax excreting hypodermal cells, 

 the wax cells, has been made in only a few species. Such cells 

 are usually more numerous during the adult than during any of 

 the nymphal stages and are fewest in number during the first 

 nymphal stage. In many genera certain wax cells are wanting 

 or are not functional until during the adult stage as the 

 genacerores of the Diaspidinae. The openings of these cells are 

 usually located on the ventral aspect of the abdomen or are 

 associated with the external opening of the oviduct, the vulva. 

 They excrete the wax in which the eggs are enclosed. 



The inner ends of the hypodermal cells are bound together 

 by a thin semicuticular layer, the basement membrane. This 

 membrane, so far as is known, does not perform any important 

 function in the Coccidae. 



The outer layer of the body-wall is the outer skeleton, cuticula, 

 or cuticle. It is generally comparatively thin and flexible in this 

 family. The cuticle and the internal skeleton are the only portions 

 not only of the body-wall but of the body remaining after the coccid 

 has been subjected to an extended treatment to caustic potash. 

 It is, therefore, incorrect to consider any of the parts remaining 

 after such a treatment as glandular structures or apply names to 

 them that would suggest such a condition. When the body is 

 studied in section, the cuticle is found to be indefinitely lamellate. 

 The outer thinner portion, hardened by the deposition of chitin- 

 is usually darker in color and inelastic. It is the outer portion 

 that is discarded when the insect molts. The much thicker inner 

 portion is elastic and permits of the increase in size or growth of 

 the body at stated intervals when the outer layer of cuticle is cast 

 off or molted. The cuticle covers not only the outer surface of 

 the body but lines the cephalic and caudal portions of the lumen of 

 the alimentary canal, the air tubes or tracheae, the ducts of the 

 salivary glands, and the caudal portion of the ducts of the repro- 

 ductive organs. It also forms the basis of the internal skeleton 



